Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Thu Apr 20 2023 Valid 12Z Sun Apr 23 2023 - 12Z Thu Apr 27 2023 ...Overview and Guidance/Predictability Assessment... An upper-level low will remian quasi-stationary over the Midwest and Northeast early next week, before weakening and splitting beneath a strengthening downstream ridge. Part of that energy may absorb back into a north-central Canadian trough while the rest may shift into the Canadian meritime mid-to-late next week. There's reasonable agreement between the operational models on the evolution of this upper pattern. Where there's more uncertainty is in the West. The latest guidance suggests that a shortwave trough will amplify over the Northwest early next week before propagating into the Plains by the middle of the week and into the East by the latter part of the week. As with recent forecasts, a model blend weighted more toward the EC/ECE/CMC was used to mitigate some of the muted and progressive signals displayed by the GFS/GEFS. A ridge will arrive along the West Coast next Tuesday/Wednesday, the strength of which will influence the development of the West/Central U.S. trough. Elsewhere, shortwave energy preceeding the amplified western trough may swing across the Gulf Coast states early-to-mid next week. ...Weather/Hazards Highlights... A pair of low pressure systems associated with the quasi-stationary mean upper-low stationed over southeastern Canada will move through the Northeast next Sunday through Tuesday. Rain showers are expected with some areas of focused heavy rainfall possible, particularly over portions of Vermont and New Hampshire, where upsloping the presence of the surface wave may support enhanced amounts. A pair of marginal risk areas, encompassing much of New England, were drawn to account for this threat, although the progressive nature of the system should make any flash flooding concerns remain low. Both systems should move into the Canadian meritime and Atlantic by next Tuesday, leaving slightly cooler temperatures in its wake from the Midwest to the Northeast. Temperatures remain springlike through the remainder of the medium range period. A low pressure system in northeastern Mexico and inverted troughing into Texas with southeasterly flow into the state will support showers and thunderstorms over across the region on Sunday. Some heavy rain rates developing inland and propagating eastward into the Gulf supported by a bit of weak upper-level energy could produce isolated instances of flash flooding over segments of southern Texas. The 00z GFS and 12z EC diverge with respect to the axis of heaviest precipitation with the GFS signalling for a northern track and the EC suggesting a more southerly solution. The day 4 marginal risk area for southern Texas was drawn with that in mind. The next system to enter Kebede Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml